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max step frequency of GRBL Atmega328p #41
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You're likely hitting the limits of grbl. Simen states that 30kHz is about as high as you can go. Keep in mind that torque drops significantly as you reduce the microstepping size. In most scenarios, you should have it as high as you can get away with. I personally run half-steps at most 10kHz, which is slightly louder but I have high torque and can run at higher speeds. |
The other thing to note about microstepping is that the supposed accuracy can be illusory. Even if the electrical signal is exact - and it's not always, depending on the driver you are using - the mechanical / electrical system may well not be keeping up with it. As you increase the microsteps and necessarily also the step rate the time the (highly inductive) driver/motor system has to reach full current gets proportionately less. Most drivers do not hit full current in the time interval allowed, thereby further reducing the torque. This is particularly true at lower voltages, such as 12v. Higher voltages increase the slew rate and therefore the max current that can be delivered in that interval. (Ironically, this makes running drivers and motors at higher voltages actually run cooler as less time is taken in switching). So if the current can't build up, the motor lags, and the "accuracy" you thought you were getting by upping the microstep rate is lost. This is a problem with many of the belt driven designs that rely on microsteps for accuracy |
I agree with Alden. I have tested many stepper drivers including mine. But many drivers lose torque at some point. One other thing I was curious about is jerky sound during movement in case of high speed seekrate. Microstep : 10 $0=200 $5=2400 ( seekrate 2400mm/min ) --> 40mm/sec There is no jerky sound during movement. But when I apply $5=3600 ( seekrate 3600mm/min ) --> 60mm/sec I supposed to capture the pulse train but I couldn't yet. Also I tried all previous version ( accellation version GRBL ) but same result I got. thank you Alden and Chamnit. By the way, is it better to apply higher voltage to stepper in case of microstepping in general ? |
You should always try to run just under the highest voltage that your What exactly do you mean by jerky motion and by it happening only On Oct 15, 2011, at 9:54 PM, pauljay
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Thank you for your comment. My machine is 300x200x60 ( X/Y/Z mm ) The motor is Tamagawa High Torque 2A 0.8degree Bipolar step motor. The step driver is IMS IM483. So when I travel X,Y, there is a jerky sound which resembles a break sound to stop momentarily. For example, when I input G0 X50. It generates the sound in the position around between 20 ~25mm. But below 20mm movement, there is no such a jerky sound. This happens in all of my stepper drivers. |
I guess this scenario might be applied in the jerky sound.
This is my guess so that i supposed to capture the step pulses in my osciloscope. |
Thanks for the info. What you state is in agreement with a problem at the end of an acceleration, which should end at about 22.5mm from the start position. And your settings seem like they should work on grbl. However, logically, the program shouldn't be losing steps after acceleration. There must be something else going on here. Although I have not run at high feedrates that you are trying to achieve. Alden: How fast have you gotten on your CNCs? Some other questions:
I will try to reproduce this problem on my end and see if I find out what's going on. There has been a report about some jerky motion at the end of acceleration before I had started working on this code. I thought I had fixed it, but it maybe something inherent in grbl that I overlooked. Pauljay, I'd really like to help you solve this, mainly to fix any grbl bugs before going to a v1.0. |
I can't reproduce this error, since my system can't go to the peak speed you have. But, I did try many different scenarios to see if I can observe it. I don't own an oscilloscope (on the list of things to buy), so I can't actually see the step pulses real time, only what my CNC mill shows me. When you say you have captured on your oscilloscope, have you actually seen this pause in step pulses at the end of acceleration? And only there? |
HI Chamnit and Alden, I found out it was because of torque. This morning simply I have applied DC36V for step driver and get the result what I want. No jerky sound during movement. I am using very slow feedrate rather seekrate is high. I have tested it on Chamnit fork of GRBL. |
I have just checked my config in terms of maths and figured out, that 24.8 steps/mm and 2500mm/min seek rate give 62kHz step rate. |
Theoretically, grbl should be able to go up to about a 100kHz step rate, but there are many many other things that can cause it to choke like the stepper interrupt slowing down the main program (parser and planner) or your motor drivers not being able to keep up. The biggest issue would crop up in cases of rapid short line segments like on curves or performing arc motions. Although depending on your system size and acceleration setting, you may never reach your maximum feed rate and your result might be hidden. If your system can do arcs/curves and work when accelerated all the way to the maximum feedrate, I would say that you have the fastest confirmed step rate reported so far. |
I am sorry. I've just found out, that I've messed m/min with m/sec, which gives humble 1kHz step rate. |
Hi everyone I have a small issue. please help me. I just start using GRBL V0.8 firmware, my board is arduino uno the stepper is a nema14 200 steps /revolution the driver is a4988, i am turning a screw with 8mm lead that means 25 steps/ mm or is it that tA is $3 command and tB is $4and $5 commands ? PS please excuse my english is not my native language |
que tengo que hacer para correr grbl a 100 khz, ?? |
Hello oleometal, Did you achieve to run grbl in 100khz? I need to run Hiwin servo drivers at 600khz ? If you have any solution, could you share with us? Thank you. |
Is there anyone who achieves more than 40KHz step frequency of GRBL Atmega328p ?
I have executed several tests changing microstep level and seekrate of each axis.
The fastest one I have succeeded in is 38.4Hkz for each axis.
If I adjust parameters to get faster speed, then interrupt handler routines went wrong.
So the pulses in my osciloscope shows broken steps.
Also the EEPROM data area is broken to show incorrect values. But it shows correctly after reseting Atmega328p board.
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